1. Field of the Invention
The invention relates to a direct injection spark ignition internal combustion engine and a method for controlling a direct injection spark ignition internal combustion engine.
2. Description of the Related Art
During homogenous combustion, if the tumble flow created in each cylinder on an intake stroke can be intensified, the tumble flow remains until the latter half of a compression stroke and then is smashed by the piston, whereby a turbulent flow is created in the cylinder, and this turbulent flow increases the combustion speed. In direct injection spark ignition internal combustion engines, the thrust force of the fuel injected into each cylinder can be utilized to intensify the tumble flow.
Meanwhile, a direct injection spark ignition internal combustion engine is proposed which performs the Atkinson cycle (Miller cycle) operation in which the time to close the intake valves is retarded so as to reduce the pumping loss and thus the fuel consumption (For example, refer to Japanese Patent Application Publication No. 2004-52551 (JP-A-2004-52551).
In typical Atkinson cycle direct injection spark ignition internal combustion engines including the one described above, the fuel injection time is set to a point before the intake stroke bottom dead center. In such engines, although fuel is injected before the intake stroke bottom dead center, the tumble flow in each cylinder can be intensified by setting the fuel injection direction appropriately, and the intensified tumble flow remains until the latter half of the compression stroke. However, if the turbulent flow in the cylinder is intensified by further intensifying the tumble flow in the latter half of the compression stroke, the combustion speed of homogenous combustion increases and thus the combustion state improves accordingly.